Stress tables, ASME

Vessels for high-temperature serviee may be beyond the temperature hmits of the stress tables in the ASME Codes. Sec tion TII, Division 1, makes provision for construction of pressure vessels up to 650°C (1200°F) for carbon and low-alloy steel and up to 815°C (1500°F) for stainless steels (300 series). If a vessel is required for temperatures above these values and above 103 kPa (15 Ibf/in"), it would be necessaiy, in a code state, to get permission from the state authorities to build it as a special project. Above 815°C (1500°F), even the 300 series stainless steels are weak, and creep rates increase rapidly. If the metal which resists the pressure operates at these temperatures, the vessel pressure and size will be limited. The vessel must also be expendable because its life will be short. Long exposure to high temperature may cause the metal to deteriorate and become brittle. Sometimes, however, economics favor this type of operation. 

Here is a inciliod lo esiimate the maximum allowable pressure for ferrous piping according to ASME and ANSI codes without referring to the actual codes stress tables. In addition, specific pipe dimensions (O.D. and thickness) need not be known, as the schedule number and pipe material are all that are necessary. 

For smooth pipe, the friction factor is a function only of the Reynolds number. In rough pipe, the relative roughness /D also affects the friction factor. Figure 6-9 plots/as a function of Re and /D. Values of for various materials are given in Table 6-1. The Fanning friction factor should not be confused with the Darcy friction fac tor used by Moody Trans. ASME, 66, 671 [1944]), which is four times greater. Using the momentum equation, the stress at the wall of the pipe may be expressed in terms of the friction factor ... 

Nominal pressure stresses shall not exceed the yield strength at temperature (see Table 10-49 and data in ASME Code, Sec. TII, Division 2). 

The maximum allowable stress values at normal temperature range for the steel plates most commonly used in the fabrication of pressure vessels are given in Table 12-3. For stress values at higher temperatures and for other materials, the latest edition of the ASME Code should be referenced. 

Some of the standards for components in Table IP-8.1 (e.g., ASME B16.9 and ASME B16.ll) state that pressure-temperature ratings are based on straight seamless pipe. Except as limited in the standard or elsewhere in this Code, such a component, made of a material having the same allowable stress as the pipe, shall be rated using not more than 87.5% of the nominal thickness of seamless pipe corresponding to the schedule, weight, or pressure class of the fitting, less all allowances applied to the pipe (e.g., thread depth and/or corrosion allowance). 

The allowable stress for occasional loads of short duration, such as surge, extreme wind, or earthquake, may be taken as the strength reduction factor times 90% of the yield strength at temperature times Mj for materials with ductile behavior. This yield strength shall be as listed in ASME BPV Code Section II, Part D, Table Y-l (ensure materials are suitable for hydrogen service see API 941), or determined in accordance with para. 

Flexibility and Stress Intensification Factors. In the absence of more directly applicable data, the flexibility factor, k, and stress intensification factor, i, shown in Appendix D of ASME B31.3 shall be used in flexibility calculations in para. IP-6.1.5. For piping components or attachments (such as valves, strainers, anchor rings, or bands) not covered in the table, suitable stress intensification factors may be assumed by comparison of their significant geometry with that of the components shown. 

C = sum of allowances for corrosion, erosion, and any thread or groove depth. For threaded components the depth is h of ASME Bl.20.1, and for grooved components the depth is the depth removed (0.02 in when no tolerance is specified). SE = allowable stress (see Table 10-44)... 

The ASME Code provides formulas that relate the wall thickness to the diameter, pressure, allowable stress, and weld efficiency. Since they are theoretically sound only for relatively thin shells, some restrictions are placed on their application. Table 18.3 lists these... 

Comprehensive tables of materials susceptible to stress corrosion cracking in specific chemicals are given by Moore (1979). Moore s tables are taken from the corrosion data survey published by NACE (1974). See also ASME BPV Code Sec. II Part D Appendix A-330. 

The maximum allowable stress values for ASME BPV Code Sec. VIII D. 1 are given in ASME BPV Code Sec. II Part D Table lA for ferrous metals and Table IB for nonferrous metals. Maximum allowable stress values for Sec. VIII 0.2 are given in Sec. II Part D Table 2A for ferrous metals and Table 2B for nonferrous metals. Different values are given for plates, tubes, castings, forgings, bars, pipes, and small sections, as well as for different grades of each metal. 

Typical maximum allowable stress values for some common materials are shown in Table 13.2. These values may be used for preliminary designs. The ASME BPV Code should be consulted for the values to be used for detailed vessel design. 

Table 13.2. Typical Maximum Allowable Stresses for Plates Under ASME BPV Code Sec. VIII D.l (The Appropriate Material Standards Should be Consulted for Particular Grades and Plate Thicknesses)...

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